An engine draws fresh air into an intake manifold through an induction system (e.g., an intake duct having an air filter). A throttle valve is implemented downstream from the air filter and controls airflow through the induction system and into the intake manifold. The air in the intake manifold is distributed to a plurality of cylinders and combined with a fuel (e.g., via port or direct fuel injection) to create an air/fuel mixture. This air/fuel mixture is compressed by pistons within the cylinders (the compression stroke) and the compressed air/fuel mixture is ignited (e.g., by spark from spark plugs). Piston rings are used to form a seal between the pistons and walls of the cylinders. The combustion of the compressed air/fuel mixture (the power stroke) drives the pistons, which rotatably turn a crankshaft to generate drive torque. Exhaust gas resulting from combustion is expelled from the cylinders into an exhaust system.
The crankshaft is housed by a crankcase that includes lubricating fluid (e.g., oil). During the compression and power strokes, the air/fuel mixture (i.e., unburnt fuel) or exhaust gas sometimes escape the combustion chamber past the piston rings and enters the crankcase, which is also known as blow-by. Crankcase ventilation systems are therefore implemented to handle these blow-by vapors, which could dilute and/or degrade the oil overtime, thereby decreasing its ability to lubricate the crankshaft. Crankcase ventilation systems typically include a positive crankcase ventilation (PCV) hose and a PCV valve to control venting blow-by vapors from the crankcase and back into the intake manifold. More specifically, engine vacuum draws the blow-by vapors from the crankcase through an oil separator (e.g., a baffle) that removes any oil from the blow-by vapors and the blow-by vapor flow through the PCV hose is controlled by the PCV valve.
Crankcase ventilation systems typically also include a make-up air (MUA) hose. This MUA hose is connected to the crankcase and to the induction system at a point upstream from the intake manifold (e.g., before the throttle valve and after the air filter). The MUA hose is used to provide fresh air to the crankcase to better flush out the blow-by vapors. Emissions standards require detection of leaks in the crankcase ventilation system, which could cause blow-by vapors (e.g., unburnt fuel or untreated exhaust gas) to be expelled into the atmosphere. One such potential leak is a disconnected MUA hose. This disconnection could occur either at the crankcase side or at the induction system side. Conventional diagnostic systems, however, are (i) not configured to detect a disconnected MUA hose, (ii) inaccurate, and/or (iii) intrusive. Accordingly, while such diagnostic systems work for their intended purpose, there remains a need for improvement in the relevant art.